Optical bistability is the phenomenon whereby an illuminated device made with a nonlinear optical material exhibits two constant light intensities at the output of the device for a given light intensity at the device input. This bistable behavior can be utilized for optical switching, optical digital memory elements, and intensity-limiting behavior, as well as transistor action (the optical counterpart of the electronic transistor). Such devices can be incorporated in all-optical communication systems, data processing systems, and logic operations in an all-optical digital computer.
First predictions of the phenomenon of optical bistability were made by A. Szoke et al, Applied Optics Letters 15, page 376 (1969); by H. Seidel, U.S. Pat. No. 3,610,731 issued in 1971; by J. W. Austin et al, Journal of Optical Society of America 61, page 650 (1971); and by E. Spiller, Journal Applied Physics 43, page 1673 (1972). The conditions for differential gain and transistor action were treated by S. L. McCall, Physical Review A, volume 9, No. 4, page 1515 (1974). This led to subsequent experiments of H. M. Gibbs et al, Physical Review Letters 36, page 113 (1976) using sodium vapor as the non-linear medium in a Fabry-Perot cavity to observe the bistable behavior and transistor type action in an all-optical experiment.
Most prior art observations of optical bistability utilized a resonator of the Fabry-Perot or ring-cavity geometry as discussed by H. J. Kimble et al, in Optical Bistability 2, Plenum Press, NY, 1984, page 1. However, as noted in Philosophical Magazine , Volumn 47, Number 4, pages 347-366 (1983), J. Hajto et al have analyzed the appearance of cavityless optical bistability in an amorphous medium due to an incident light-induced, temperature-dependent, increase of the absorption in the medium. This phenomenon was also subsequently observed in a GaAs multiple quantum well semiconductor material by D. A. B. Miller et al, as noted in Optics Letters, Volume 9, Number 5, page 162 (1984); and was also observed in the semiconductor CdS by tuning near the bound exciton resonance by M. Dagenais et al in Applied physics Letters 45, page 210 (1984). These experiments disclose two essential attributes of an optical bistable material: (a) nonlinear dependence of the steady-state temperature at the boundaries on the light intensity, and (b) nonlinear renormalization of the absorption resonance due to the temperature rise in the medium. These devices produce mirrorless (cavityless) optical bistability with single hysteresis loops, for the output versus input intensities, in the clockwise direction when the input field is swept past the hysteresis zone and returned to a low intensity again.